Heat exchanger drip tube

ABSTRACT

A drip tube has a generally horizontal section, a generally vertical section and a drip loop connecting the sections. The drip loop is positioned so that its exterior surface is lower than the exterior surfaces of the generally horizontal section and the generally vertical section at the points where they meet the drip loop to provide a location where water may drip.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No. 61/127,513, filed on May 14, 2008 and entitled “Heat Exchanger Drip Tube.”

BACKGROUND

Advances in microchannel heat exchanger technology have demonstrated its advantages over the previously more conventional round-tube plate-fin type heat exchanger. Some of the benefits provided by microchannel heat exchangers include a reduction in the amount of refrigerant required for operation, more efficient heat transfer, and a reduced footprint. Microchannel heat exchangers, once used primarily in automotive applications, are now also finding use in residential and commercial air conditioning and refrigeration applications. Microchannel heat exchangers generally use all aluminum coils. In many applications, however, refrigerant enters and leaves the coils via copper tubes. A heat exchange system with aluminum and copper surfaces may run into problems with galvanic corrosion.

Galvanic corrosion occurs when two dissimilar metals make contact with one another in the presence of an electrolyte thereby forming a galvanic couple. The more noble metal (higher on the galvanic series) provides the surface area for the reduction reaction and the less noble metal (lower on the galvanic series) corrodes in an oxidation process. The oxidation occurs in the greatest amount at the interface of the two metals but may also occur at some distance away from the actual interface. In coastal regions, the most common electrolyte is salt water in the air. A fine salt water mist may be blown inland for up to fifty miles from the coast. Sulfur dioxide from industrial pollution also creates an electrolyte when it combines with moisture in the air.

If the two dissimilar metals in a heat exchanger are physically separated from one another, no interface exists for corrosion to occur. However, water containing particles of copper may come into contact with aluminum surfaces of the heat exchanger and form a galvanic couple. In some residential and commercial refrigeration systems, for example, the condenser section(s) of the heat exchangers used in vapor compression refrigeration are located outdoors (e.g., outside the residence, on the rooftops of commercial buildings). These condensers can be exposed to rain, snow, sleet, and salt. The water or moisture present in the outdoor environment has the potential to carry copper particles into contact with aluminum surfaces of the condenser such as the coils or the manifolds. Galvanic corrosion can occur in the areas where copper and aluminum make contact.

SUMMARY

Exemplary embodiments of the invention include a system having a heat exchanger manifold and a drip tube in fluid communication with the manifold. The drip tube includes a generally horizontal section, a generally vertical section, and a drip loop connecting the horizontal and vertical sections. The horizontal section, vertical section, and drip loop each have an exterior surface. A portion of the drip loop exterior surface is positioned so that it is lower than the exterior surfaces of the horizontal and vertical sections where the horizontal and vertical sections meet the drip loop.

A further embodiment of the present invention includes a method for protecting aluminum surfaces of a heat exchanger. The method includes shaping a drip tube having a generally horizontal section, a generally vertical section, and a drip loop connection the horizontal and vertical sections. The drip tube is shaped so that an exterior surface of the drip loop is positioned lower than the exterior surfaces of the horizontal and vertical sections where the horizontal and vertical sections meet the drip loop. The method also includes connecting the horizontal section of the drip tube to a heat exchanger manifold and connecting the vertical section of the drip tube to a refrigerant line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a refrigerant vapor compression system incorporating a heat exchanger with a drip tube.

FIG. 2 is a perspective view of part of a heat exchanger showing a manifold connected to an inlet tube and a drip tube.

FIG. 3 is a side view of a heat exchanger manifold connected to a drip tube.

FIG. 4 is a cross-section view of a heat exchanger manifold connected to a drip tube via a belled section with a barrier layer.

DETAILED DESCRIPTION

Illustrated in FIG. 1, is an example of a refrigerant vapor compression system 100. The system includes evaporator 102, compressor 104, condenser 106, and expansion valve 108. Refrigerant lines connect the components of the system described above. Fans 110 and 112 direct air across the evaporator 102 and condenser 106, respectively, as part of the heat transfer system. The condenser 106 includes manifold 12, which is connected to inlet tube 16 and drip tube 18. While FIG. 1 illustrates drip tube 18 connected to condenser 106, drip tube 18 could also be connected to an evaporator such as evaporator 102.

Illustrated in FIG. 2, is part of a heat exchanger section 10 having a manifold 12 and a plurality of microchannel flow paths 14. Heat exchanger section 10 may function as an evaporator or as a condenser depending on the desired heat transfer application. Generally, heat exchanger section 10 is located outdoors (e.g., outside a residence, on the rooftop of a commercial building), but heat exchanger section 10 may also be located indoors. Microchannel flow paths extend from manifold 12 to another manifold (not shown). Manifold 12 may be either an inlet or outlet manifold. Manifold 12 and microchannel flow paths are generally aluminum.

Attached to manifold 12 are inlet and outlet tubes. In the embodiment shown in FIG. 2, inlet tube 16 is connected to manifold 12 near the top of the manifold. Inlet tube 16 also connects with a refrigerant line (not shown) in the closed heat exchanger circuit. Drip tube 18 is connected to manifold 12 near the bottom of the manifold. Drip tube 18 also functions as an outlet tube in the embodiment illustrated in FIG. 2. While FIG. 2 illustrates inlet tube 16 at the top of the manifold and outlet drip tube 18 at the bottom, other embodiments are possible. For example, tube 16 could function as an outlet and drip tube 18 could function as an inlet. In either case, the tube functioning as the drip tube will generally be located lower on the manifold than the other tube regardless of which is the inlet or outlet. It is also possible for both tubes (inlet and outlet) connected to the manifold to be drip tubes.

Drip tube 18 includes horizontal section 20, drip loop 22, and vertical section 24. As illustrated in FIG. 2, at least a portion of horizontal section 20 is generally horizontal and generally perpendicular to heat exchanger manifold 12 and vertical section 24. Horizontal section 20 connects directly with manifold 12 or is inserted into a belled section 26, which is connected to manifold 12, as shown in FIGS. 2-4. At least a portion of vertical section 24 is generally vertical and perpendicular to at least a portion of horizontal section 20. Vertical section 24 connects with a refrigerant line (not shown) in the closed heat exchanger circuit. Drip loop 22 connects horizontal section 20 and vertical section 24. Drip tube 18 is generally copper, but other metals such as aluminum may be used. Drip tube 18 functions as an inlet or an outlet for manifold 12. Refrigerant travels through the inner passage of drip tube 18 to or from manifold 12.

As illustrated by FIG. 3, drip loop 22 is a generally U-shaped loop located between horizontal section 20 and vertical section 24. In the embodiment shown in FIG. 3, drip loop 22 slopes in a slight downward direction from horizontal section 20 to form one half of the U shape. Drip loop 22 then curves upward towards vertical section 24 to form the other half of the U shape. Drip loop 22 includes a bottom exterior surface 28. At least a portion of the bottom exterior surface 28 is positioned lower than the exterior surfaces of horizontal section 20 and vertical section 24 where the horizontal section 20 and vertical section 24 join drip loop 22. In some embodiments it is possible for horizontal section 20 and vertical section 24 to have exterior surfaces lower than bottom exterior surface 28, but these surfaces cannot be located where horizontal section 20 and vertical section 24 join with drip loop 22. The lowest portion of bottom exterior surface 28 provides a location where water may collect, form a droplet, and drip.

In one exemplary embodiment of drip tube 18, drip tube 18 has an outer diameter of about 9.5 mm. The wall thickness of drip tube 18 is about 0.7 mm. Vertical section 24 of drip tube 18 is about 42 mm in length. The straight sloped portion of drip loop 22 (the portion between horizontal section 20 and the sharp bend in drip loop 22) is about 19 mm in length. Drip loop 22 slopes downward from horizontal section 20 at an angle of about 19° and the U-bend of drip loop 22 traverses an arc of about 109°. The distance between the centerpoint of manifold 12 and the centerpoint of vertical section 24 is about 76 mm. Horizontal section 20 connects with manifold 12 about 40 mm above heat exchanger bottom surface 30. The dimensions of other embodiments of drip tube 18 may vary. For example, the outer diameter of drip tube 18 may be between about 2.0 mm and about 25.4 mm. Wall thickness may be between about 0.1 mm to about 4 mm. The angles and lengths of the different portions of drip tube 18 may be adapted to the particular needs of the heat exchanger manifold and refrigerant lines. However, all embodiments will be configured so that the drip loop has an exterior surface lower than the exterior surfaces of the horizontal and vertical sections where they connect to the drip loop.

Water and moisture (from rain, snow, or condensation) that collect in heat exchanger section 10 may accumulate on exterior surfaces of refrigerant lines in fluid communication with drip tube 18. Water may travel down the exterior surfaces of the refrigerant lines towards the heat exchanger manifold 12. As refrigerant lines are often made of copper, this water may collect particles of copper as it travels along the exterior surfaces of the refrigerant lines. In a heat exchanger without a drip tube, the copper-containing water may travel to the area where the refrigerant line (inlet/outlet) connects with the aluminum heat exchanger manifold 12. The copper and aluminum may form a galvanic couple and galvanic corrosion may occur at or near the area where both copper and aluminum are present.

The drip tube 18 prevents copper-containing water from reaching the manifold 12. Water travels down the exterior surface of a refrigerant line and vertical section 24 of drip tube 18. The water then reaches drip loop 22 and continues to the lowest portion of bottom exterior surface 28. The water will drip from the lowest portion of bottom exterior surface 28 rather than continue along drip loop 22 to horizontal surface 20 and eventually to manifold 12. The water would need to travel “uphill” to reach horizontal surface 20 from drip loop 22. Gravity will cause the water to form droplets and drip from the lowest portion of bottom exterior surface 28 before it can reach horizontal surface 20.

While FIG. 3 illustrates a U-shaped drip loop 22, other configurations that provide a bottom exterior surface 28 that is lower than the exterior surfaces of horizontal section 20 and vertical section 24 where horizontal section 20 and vertical section 24 join with drip loop 22 are possible. For example, drip loop 22 may also have a V-shaped section as long as the lowest point of the V is lower than the exterior surfaces of the horizontal section 20 and vertical section 24 where horizontal section 20 and vertical section 24 join with drip loop 22.

Water drips from bottom exterior surface 28 of drip loop 22 onto heat exchanger bottom surface 30. In exemplary heat exchanger embodiments, bottom surface 30 directs collected water away from manifold 12. Bottom surface 30 may be sloped to facilitate collection of water in areas of heat exchanger section 10 away from manifold 12 where it is allowed to evaporate or drain out of heat exchanger section 10.

One embodiment of a connection between drip tube 18 and manifold 12 is illustrated in FIG. 4. Belled section 26 is used to facilitate the connection of manifold 12 and drip tube 18. In some embodiments, belled section 26 may be omitted and drip tube 18 is connected directly to manifold 12. Belled section 26 is generally aluminum, but other metals, such as copper, may also be used. One end of belled section 26 is positioned within an opening in the wall 32 of manifold 12. Horizontal section 20 of drip tube 18 is positioned in the other end of belled section 26. Once connected, the inner passages of manifold 12 and drip tube 18 are in fluid communication.

Manifold 12 and belled section are typically similar metals in this construction. Belled section 26 and horizontal section 20 of drip tube 18 are typically dissimilar metals. To prevent galvanic corrosion between belled section 26 and drip tube 18, one or more barrier layers 34 may be employed. Barrier layer 34 is positioned around the joining area of belled section 26 and drip tube 18 to protect the area where dissimilar metals contact one another from water and oxygen, thereby preventing or reducing the opportunity for galvanic corrosion. Barrier layer 34 is generally placed around belled section 26 or drip tube 18 after connection with manifold 12. Barrier layer 34 may be a shrink wrap that seals around belled section 26 when heat is applied to the shrink wrap. Barrier layer 34 may be any material appropriate to protect metals from water and oxygen, such as rubber, neoprene, nylon, or latex.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A system comprising: a heat exchanger manifold; and a drip tube in fluid communication with the heat exchanger manifold, the drip tube comprising: a generally horizontal section having an exterior surface; a generally vertical section having an exterior surface; and a drip loop having an exterior surface and connecting the horizontal section and the vertical section, wherein a lowest portion of the drip loop exterior surface is positioned lower than the horizontal section exterior surface where the horizontal section and drip loop meet and lower than the vertical section exterior surface where the vertical section and drip loop meet.
 2. The system of claim 1, wherein the heat exchanger manifold and the drip tube are similar metals.
 3. The system of claim 1, wherein the heat exchanger manifold and the drip tube are dissimilar metals.
 4. The system of claim 3, wherein the heat exchanger manifold is aluminum and the drip tube is copper.
 5. The system of claim 1, wherein the drip tube is an inlet or an outlet for the heat exchanger manifold.
 6. The system of claim 1, wherein the horizontal section is generally perpendicular to the heat exchanger manifold.
 7. The system of claim 1, wherein the horizontal section is connected to the heat exchanger manifold.
 8. The system of claim 1 further comprising a belled section, wherein the belled section connects the heat exchanger manifold and the drip tube.
 9. The system of claim 1 further comprising a barrier layer, wherein the barrier layer surrounds a portion of the heat exchanger manifold and a portion of the drip tube.
 10. The system of claim 8, further comprising a barrier layer, wherein the barrier layer surrounds a portion of the belled section and a portion of the drip tube.
 11. A heat exchanger section comprising: first and second manifolds; a plurality of flow paths extending between the first and second manifolds; and at least one drip tube in fluid communication with at least one manifold, the drip tube comprising: a generally horizontal section having an exterior surface; a generally vertical section having an exterior surface; and a drip loop having an exterior surface and connecting the horizontal section and the vertical section, wherein a lowest portion of the drip loop exterior surface is positioned lower than the horizontal section exterior surface where the horizontal section and drip loop meet and lower than the vertical section exterior surface where the vertical section and drip loop meet.
 12. The heat exchanger section of claim 11, wherein the at least one drip tube and the at least one manifold in fluid communication with the at least one drip tube are dissimilar metals.
 13. The heat exchanger section of claim 12, wherein the at least one drip tube is copper and the at least one manifold in fluid communication with the at least one drip tube is aluminum.
 14. The heat exchanger section of claim 11, wherein the at least one drip tube is an inlet or an outlet for the at least one manifold in fluid communication with the at least one drip tube.
 15. The heat exchanger section of claim 11, wherein the horizontal section is connected to the at least one manifold in fluid communication with the at least one drip tube.
 16. The heat exchanger section of claim 11 further comprising a belled section, wherein the belled section connects the at least one drip tube and the at least one manifold in fluid communication with the at least one drip tube.
 17. The heat exchanger section of claim 11 further comprising a barrier layer, wherein the barrier layer surrounds a portion of the at least one drip tube and a portion of the at least one manifold in fluid communication with the at least one drip tube.
 18. The heat exchanger section of claim 11 further comprising a barrier layer, wherein the barrier layer surrounds a portion of the belled section and a portion of the at least one drip tube.
 19. A method for protecting aluminum surfaces of a heat exchanger, the method comprising: shaping a drip tube comprising a generally horizontal section, a generally vertical section, and a drip loop connecting the horizontal and vertical sections, wherein the drip tube is shaped so that an exterior surface of the drip loop is positioned lower than an exterior surface of the horizontal section where the horizontal section and drip loop meet and lower than an exterior surface of the vertical section where the vertical section and drip loop meet; connecting the horizontal section of the drip tube to a heat exchanger manifold; and connecting the vertical section of the drip tube to a refrigerant line.
 20. The method of claim 19 further comprising providing a barrier layer to a portion of the drip tube and a portion of the heat exchanger manifold.
 21. The method of claim 19, wherein the step of connecting the horizontal section of the drip tube to a heat exchanger manifold further comprises: connecting a first end of a belled section to the heat exchanger manifold; and connecting the horizontal section of the drip tube to a second end of the belled section.
 22. The method of claim 21 further comprising providing a barrier layer to a portion of the drip tube and a portion of the belled section. 